Man and Mollusc - Cephalopoda (Squid and octopi) - Phylum Mollusca. Cuttlefish Nautilus All my cousins and I have large heads and very complex brains. We also have two eyes and use them to see almost as you humans do (Our optical nerve is of particular interest, being amazingly large. It has been used to study how optical nerves work). We can think through fairly complex puzzles (like where you hid some food in a maze) and remember how to solve them faster the next time. The only cephalopod with a true shell is the chambered nautilus. The argonaut has a shellac-like structure but this not a true shell. It is but a brood case (sort of cradle) to hold the eggs until the young hatch. This case is not attached to the animal and is held in place with one pair of her tentacles. After the Agonauta (the argonaut genus) mother is through with this egg case, it is left to float on the ocean, and is often picked up by men, who call it a "paper nautilus".

Argonaut egg case Picture courtesy of Guido Poppe We have cells in our skin, called chromataphores, which enable us to rapidly change our skin color and pattern whenever we want to. Example: if we get mad, we go a blotchy red color; if afraid we go a very pale almost white color. We can change our skin color and pattern to match our surroundings as well; this is called being able to camouflage ourselves. If an enemy threatens us, we squirt out a cloud of purple-black ink, which confuses them and we jet away. This ink is also toxic or poisonous to our enemies such as sharks. We all have arms modified with sucker discs with which we capture, hold and pull our food to our hard parrot-like-beak of a mouth. Octopus have eight of these tentacles. Squid have ten (called decapods) tentacles. The cuttlefish and nautilus have many. If we ever lose one of these tentacles in a fight or due to an injury, we just grow a new one! The tips of these tentacles are so sensitive that we can tell the difference in size, shape and texture of objects. I and all my cousins breath through gills, and have three hearts.

We are all carnivorous predators (we catch live food) eating such things as other molluscs, fish and other marine invertebrates. We crush our food in our hard bill then rasp off bits with the radula (like a fingernail file) located in our mouths. Most cephalopods have separate sexes and fertilization is internal. The males produce a "sperm packet" which he places inside the female s body using one of his tentacles. Sometime later, the female then lays eggs. Many cephalopods are good mothers and stay with their eggs until they hatch. They keep clean, fresh water flowing over the eggs and caress them to keep them clean of derbies. The young hatch out as perfect small copies of their parents. (See Avril meets Charlie face to face) Here are some interesting Cephalopod facts: Cephalopods first appeared about 500 million years ago. Some cephalopod cans swim faster than fish. The giant squid living deep in our oceans do battle with largest whales and may eat large sharks.

These giants can reach a striking 1,600 kilograms (nearly a ton!) and be 18 meters (60 feet) long - but many suspect the biggest ones haven't been found yet!!! Sperm whales battle and eat these monsters of the deep at depths up to a km (over half a mile) below the surface - but there is evidence that sometimes the Giant Squid win the battle... Octopus can squeeze their bodies through remarkably small openings. A large octopus could easily crawl through a pop can that had been opened at both ends. The internal structure (long oval chalky "bone") of the cuttlefish is used in birdcages as a dietary supplement and for keeping their beaks in good condition. The Cephalopoda The Cephalopoda close FUN FACT: From the dark abyss to shallow tide pools, research has recently revealed some of the mysterious behaviors of two famed cephalopods, the Giant Squid and the deadly Blue-ringed octopus (click image below for an enlargement). Cephalopods are the most intelligent, most mobile, and the largest of all molluscs.

Squid, octopuses, cuttlefish, the chambered nautilus, and their relatives display remarkable diversity in size and lifestyle with adaptations for predation, locomotion, disguise, and communication. These "brainy" invertebrates have evolved suckered tentacles, camera-like eyes, color-changing skin, and complex learning behavior. Their lengthy evolutionary history spans an impressive 500 million years and the abundant fossils they've left behind (mostly shelled nautiloids and ammonoids) record repeated speciation and extinction events. From myths about their enigmatic fossilized remains to fantastic accounts of tentacled sea monsters, cephalopods also figure prominently in the literature and folklore of human societies around the world. Today, biologists and paleontologists continue to captivate the human mind and imagination with details of these molluscs' behavior, natural history, and evolution. Fossil record There are about 17,000 named species of fossil cephalopods, compared to the 800 identified living species of cephalopods. Clearly the lineages of extinct taxa were prolific and diverse.

So diverse in fact, that paleontologists have identified three distinct fossil clades that are entirely extinct: Endoceratoidea, Actinoceratoidea, and Bactritoidea (cladogram A, at right). All members of these clades were squid-like, but had straight external shells called orthocones. They flourished in Paleozoic oceans between the Ordovician (488 mya) and Triassic periods (200 mya) with shells that, in some species, reached nearly 10 meters in length. More familiar to us in the fossil record are the nautiloids, ammonoids, and belemnites. Nautiloids and ammonoids Nautiloids are the earliest cephalopods found in the fossil record, appearing by the Late Cambrian . The earliest forms were orthoconic (having straight shells), but during the Ordovician the nautiloids experienced a rapid diversification and evolved a planispiral (coiled in a single plane) shell shape. All have shells with nacre and interconnected internal chambers, similar to what we see in the modern nautilus.

This morphology is very similar to many of the ammonoids, which first appear in coiled form in the Devonian Period. Though nautiloids and ammonoids may appear the same, they are easily distinguished by the location of their siphuncle and the shapes of their sutures. The photo on the left shows the position of the siphuncle in ammonoids. The other two are of nautiloids exhibiting the simple sutures typical of the group. The siphuncle is an internal tube that runs through and connects the chambers of the shell. In nautiloids, it runs through the center of the shell chambers, while in almost all planispiral ammonoids, it is found along the shell's outer edge (above left). Sutures are contact lines between shell chamber walls (called septa) and the inner shell wall of nautiloid and ammonoid shells. In nautiloids these lines are straight and are called simple sutures (above center and right). In contrast, ammonoid sutures dip and fold in undulations called lobes and saddles (below left). The most undulated, complex sutures are found in the prolific ammonoids of the Cretaceous , the ammonites (below right).

One pattern of change in the evolution of ammonoids as a clade is that their suture morphology became more complex with time. That is, ammonoids from the Cretaceous have sutures with more intricate lobes and saddles than those of their relatives from the Permian 200 million years earlier. Hildoceras bifrons (left) illustrates the typical lobes and saddles of ammonoid sutures. The sutures on the ammonite (right) are even more complex. FUN FACT: Ammonoids, like belemnites, have also played a notable role in folklore. During the Middle Ages, their coiled shells were interpreted by the English, who encountered them in Jurassic-aged rocks exposed throughout Great Britain, as lithified snakes (called "snake stones"). Similarly, ammonite fossils encountered by the early Romans were mistaken for horns, and termed "ammonites" for the coiled horns of the Egyptian ram-god Ammon. Suture patterns and lifestyle: The diversity of this suture geometry has inspired paleontologists to investigate its function. In one study, paleontologists (Daniel et al.

1997) used modeling to determine if there was a relationship between the pattern of lobes and saddles and buoyancy and the ability to withstand pressure. They found that simple sutures, like those in nautiloids and early ammonoids, can withstand great pressure but have poor buoyancy control. They interpret that these animals lived at depth and were not fast moving. In contrast, complex sutures like those in ammonites of the Cretaceous did not withstand pressure well, but allowed for very effective buoyancy control. They infer that this reflects a lifestyle at shallower depths. Based on this evidence, it appears that many ammonoid lineages evolved over millions of years, beginning in deep water habitats and evolving to inhabit relatively shallow ones. Shell morphology: Another characteristic unique to ammonoid cephalopods is that although most were planispiral, the shells of some species were wide, open-coiled, kinked, twisted, or hooked. The implications of these shapes on the animals' behavior and lifestyle could be profound, but how could it be tested? The answer is through inference. One way paleontologists infer function from an organism's shape or form, is through experimentation and comparison with living animals.

In this case, paleontologists measured buoyancy and hydrodynamic characteristics of Nautilus, and compared their results to actual tests of ammonoid shells and models in a water flume. They found that planispiral shell shapes (like a discus) were able to move through the water quickly, while wider and more open shell shapes moved more slowly. These morphologies could mean that planispiral cephalopods lived an active, pelagic lifestyle and wider shelled ammonoids lived near the ocean bottom and were slow movers. Dramatic curves, twists, as well as highly ornate ammonoid shells also suggest that those animals were relatively slow movers inhabiting a quiet marine environment. Belemnites The rostrum of belemnites is the part most frequently preserved (left). At right, a long belemnite rostrum in a block containing other marine fossils. The fossil record of most cephalopods in the clade Coloidea (squid, cuttlefish, octopuses, and their relatives) is poor, especially when compared to their shelly relatives. Their hard parts, if any, are internal, can be greatly reduced in size, and often lack calcification.

The extinct belemnites, however, are the exception. These squid-like animals (below) swam with ammonoids and nautiloids in oceans of the Triassic, Jurassic , and Cretaceous Periods and are considered by paleontologists to be the ancestors of the Coleoidea. Like orthocones, belemnites had a straight shell, but it was internal, not external. It was made of three parts, a proostracum and phragmocone followed by a rostrum. Being highly resistant, the posterior bullet-shaped rostrum is most often preserved and can be found in great quantity and concentration in Mesozoic marine sediments (see photos). Before these bullet-shaped fossils were understood as fossils, early Europeans explained them as the products of lightning hitting the ground and named them "thunderbolts" or "thunderstones." Despite the great diversity in size, shell morphology, behavior, and lifestyle, cephalopods are all united by a suite of shared molluscan characters. They are marine, predatory, and have at least eight arms derived from the molluscan foot. All have a modified radula, and a horny, parrot-like beak for subduing prey.

Their mantle is modified into a siphon for movement via jet-propulsion, and their highly developed nervous and sensory systems include complex eyes and a centralized brain. Their name, Cephalopod or "head-foot" in Greek, reflects the unique relationship between the cephalopod head and foot: the arms encircle the animals' head. Life history & ecology Three main clades are typically identified within the Cephalopoda (cladogram B, left): the Ammonoidea (an extinct and shelled clade), Nautiloidea (with only one living shelled genus, Nautilus) and Coleoidea (squids, cuttlefish, octopuses, the Ram's Horn Squid, the "paper nautilus," and an extinct clade, the belemnites). The ammonoid lineage survived for 300 million years in the oceans of the Paleozoic and Mesozoic. Most had planispiral (coiled in a single plane) external shells, and throughout their evolutionary history these plentiful predators shared the seas with the nautiloids, a clade of less diverse shelled cephalopods.

By the end of the Cretaceous Period however, extinction had wiped out the ammonoids entirely and left only one surviving nautiloid clade, the genus Nautilus. Today, the only living representatives of shelled cephalopods are a few species of Nautilus. These molluscs are slow-moving, restricted to deep water, and have coiled shells that are similar to those of their fossil ancestors. From left, the exterior shell of the extant Nautilus; a cross-section of the Nautilus shell; the internal shells of the Ram's Horn Squid (Spirula spirula); and the secreted external papery shell-like brood pouch of the female Paper Nautilus (Argonauta sp.). A female Octopus digueti. Members of the Coleoidea are probably the best known of the Cephalopoda, as this group contains the squids (Teuthoidea) and octopuses (Octopoda) (right).

Also included in this clade are the lesser-known cuttlefish (Sepioidea), the Ram's Horn Squid, which has an internal coiled shell and floats head down in the water, and an enigmatic deep water genus called the "vampire squid" (Vampyromorpha). The majority of coleoids are squid species, and most of these animals are torpedo-shaped, fast moving, and have a thin, flexible internal shell called a pen. Cuttlefish (sometimes called "cuttles") look like squid, but have stouter bodies with a broad internal shell called a cuttlebone or sepion. They move mostly by undulating their body fins and can live in the water column or at the sediment surface. Octopuses are adapted to a benthic lifestyle, have no shell, can mimic their surroundings, and even "walk" on two of their eight arms. Belemnites are sometimes considered the sister group of extant (living) coleoids, but have also been interpreted as their ancestor.

FUN FACT: In 2006, a UC Berkeley graduate student reported that the Indonesian Coconut Octopus, Octopus marginatus, can move along the ocean floor using only the tips of its arms, almost like "walking." See Crissy Huffard's " Walktopus ." Based on molecular and morphological data, the extant Coleoidea is a monophyletic group (cladogram C, below). It is the sister group of the living species of Nautilus, which is also a monophyletic clade, albeit of only a few species (D, below). The phylogenetic relationships within the coleoids is less clear. Some cladograms depict the Sepioidea (cuttlefish), Teuthoidea (squid), Vampyromorpha (vampire "squid"), and Octopoda (octopuses) as coupled into two sets of sister groups, the Decabrachia and Octopodiformes (E, below). While the cladograms from another study (Lindgren et al.

2004) illustrate that although the coleoids are monophyletic , the cuttlefish (Sepiodea) are nested within the squids (Teuthoidea), making the Teuthoidea clade paraphyletic (F, below right). More on morphology The external shell. One of the most obvious differences in body type, which for cephalopods does reflect shared ancestry, is the presence or absence of an external shell. Clades without an external shell are called endocochleate and include the coleoids; squids, cuttlefish, and octopuses. The internal shell of these taxa, called a gladius, can be cartilaginous, calcareous, chitinous or absent entirely. Presence of an external shell, such as that of the Nautiloids, Ammonoids, and orthoconic cephalopods, is considered a plesiomorphic , or ancestral state. The eye. No presentation of cephalopods would be complete without a discussion of the cephalopod eye. This structure is probably the most sophisticated eye of all invertebrates and is as complex as the vertebrate eye, though the two are not homologous .

For their body size, cephalopod eyes are relatively large. They contain an iris, pupil, and lens, but not necessarily a cornea. Octopuses are the only cephalopods with a completely protected "closed" cornea. That means that the eyes of squids and sepioids (cuttlefish, etc.) are in direct contact with sea water! The pupil in cephalopods is unique in that its morphology is different in octopuses, cuttlefish, and squid. Octopuses have a slit-shaped rectangular pupil. In cuttlefish it is W-shaped, and in squid it is round (see below). In Nautilus the eye is much simpler. It is mounted on a stalk, has no lens, and has a very small pupil (1-2 mm). It can narrow and widen in different brightnesses but resolves images poorly, so probably is useful only to detect light. Differing eye morphologies in cephalopods. From left, a squid (Loligo), octopus, cuttlefish, and Nautilus.

Note the hyponome below the octopus eye  this is a muscular tube, that when contracted, expels water in a jet, propelling the octopus backwards. The hyponome can be aimed in various directions, giving the octopus finer control over its escape route. Arms and tentacles. Arms and tentacles are another distinguishing cephalopod characteristic. All cephalopods have arms, but not all cephalopods have tentacles. Octopuses, cuttlefish, and squid have eight non-retractable arms, but only cuttlefish and squid (Sepioidea and Teuthoidea) have tentacles (two each). Arms usually have cirri (fleshy papillae/palps), often suckers, and sometimes hooks (modified suckers) along their undersides. These can be attached to the arm directly or by a flexible stalk and are used to adhere to substrates and catch prey. Tentacles are longer than arms, are retractable, and usually have a blade-shaped or flattened tip, called a club, which is covered in suckers. Squid and cuttlefish have one pair of tentacles and they use these to strike quickly at prey.

FUN FACT: The largest cephalopod Mesonychoteuthis hamiltoni, (Fig. 17) called the colossal squid, is longer than a city bus, while the smallest cephalopod, Idiosepius notoides , the pygmy squid, could fit on your fingernail. Sex and reproduction. Sex and reproduction in cephalopods is in many ways quite different than in other molluscs. First, sexes are separate and mating usually includes a courtship that often involves elaborate color changes. This is followed by the transfer of a spermatophore (sperm packet) by a male to a female through her mantle opening. The spermatophore is transferred by the male using either a penis or a modified arm called a hectocotylus. Most females then lay large yolky eggs in clusters on the ocean floor or on any other hard substrate. Eggs develop by dividing unequally instead of in the spiral pattern of other molluscs. It is thought this is a derived mode of development. After a period of development within the egg, juveniles hatch out directly without the swimming larval stage common to many other molluscs. Most males and females die shortly after spawning.

FUN FACT: A hectocotylus is a cephalopodic arm of a male, modified to deliver a spermatophore (sperm-containing sac) to a female. In some taxa, part of this arm can detach from the male and remain inside the female. In 1829, the famous naturalist George Cuvier first identified and described a hectocotylus in the paper nautilus (an octopus of the genus Argonauta) but, at the time he thought that this detached arm was a parasitic worm! He named it Hectocotylus octopodis. When it was discovered that the "worm" was really a cephalopod arm, the name "hectocotylus" was kept but its meaning changed to refer to the spermatophore-transferring arm of any male cephalopod. Top: The chromatophores on this three-millimeter-long, 12-hour-old baby blue-ring octopus are clearly visible.

Bottom: Click on this photo to see an enlargement  you'll need to in order to see the chromatophores (the dark stippling) on the skin of this California Two-spot Octopus (Octopus bimaculoides). Changing color. Cephalopods have an amazing ability to change color very rapidly. They accomplish this feat using numerous pigment-filled bags, called chromatophores. Chromatophores are found in the skin, and expand and contract to reveal or conceal small dots of color (left). They can be so densely concentrated that 200 may be found in a patch of skin the size of a pencil eraser! Additionally, an iridescent dermal tissue can also be manipulated by some cephalopods to aid in camouflage, courtship rituals, or accompany color changes. Some pelagic squids possess an additional color-changing structure; the light organ. A pair of these light organs is located within the mantle cavity on the underside of the squid. Each contains a crypt and a lens. A crypt is a small sac that houses luminous bacteria and a lens is a complex stack of tiny reflecting plates that controls the luminescence of this bacteria.

Light from the bacteria projects downward and the squid can manipulate its intensity to match any light coming from above. This masks the squid's own silhouette, protecting it from potential predators. The brain. Finally, one of the most intriguing aspects of cephalopods is their intelligence. With a centralized brain, the largest of all invertebrates, and highly developed eyes and other sense organs, they are able to remember and learn by example or through trial and error. References and resources Daniel, T.L., B.S. Helmuth, W.B. Saunders, and P.D. Ward. 1997. Septal complexity in ammonoid cephalopods increased mechanical risk and limited depth. Paleobiology 23(4):470-481. Lee, P.N., P. Callaerts, H.G. de Couet, and M.Q Martindale. 2003. Cephalopod Hox genes and the origin of morphological novelties. Nature 424:1061-1065. Lindgren, A.R., G. Giribet, and M.K. Nishiguchi. 2004.

A combined approach to the phylogeny of Cephalopoda (Mollusca). Cladistics 20(5):454-486. Mangold (1922-2003), K.M., and R.E. Young. 1996. Idiosepiidae Appellof, 1898. Pygmy squids. in The Tree of Life Web Project, . Ruppert, E.E., R.S. Fox, and R.D. Barnes. 2004. Invertebrate Zoology : A Functional Evolutionary Approach. Brooks Cole, California. 963 pp. Sual, L.R., and C.J. Stadum. 2005. Fossil Argonauts (Mollusca: Cephalopoda: Octopodida) from late Miocene siltstones of the Los Angeles basin, California. Journal of Paleontology 79(3):520-531. Wei, S.L., and R.E. Young. 1989.

Development of symbiotic bacterial bioluminescence in a nearshore cephalopod, Euprymna scolopes. Marine Biology 103:541-546. Web resources cephalopod | Definition, meaning & more | Collins Dictionary Definitions noun 1. any marine mollusc of the class Cephalopoda, characterized by well-developed head and eyes and a ring of sucker-bearing tentacles . The group also includes the octopuses , squids , cuttlefish , and pearly nautilus adjective also: cephalopodic, cephalopodous (ˌsɛfəˈlɒpədəs ) 2. of, relating to, or belonging to the Cephalopoda Collins English Dictionary. Copyright © Harper Collins Publishers Derived forms Octopuses (Octopodidae) Octopuses (Octopodidae) A giant octopus' (E. dolfleini) suckers. Picture: Sami Laine from kelpdiver.com . The name "octopus" comes from the Greek. It means eight-foot, and that also makes an octopus special among other cephalopods.

Where a squid or a cuttlefish has got ten arms, an octopus has got eight. In that regards, octopuses have something in common with their nearest relatives, the argonauts , which also have got eight arms. The number of their arms is not the only thing, which separates octopuses from other cephalopods. It is also the absence of a shell. All cephalopods, leaving aside the ancient Nautilus, which still has got an external shell, have got the tendency to reduce their shell, so squids only have left an internal sword-shaped structure called the gladius and cuttlefish have their internal cuttlebone, also a remainder of a shell. Octopuses have got neither, they lack any trace of a shell, internal or external. Picture: Robert Patzner , Salzburg University . Without an inner shell, octopuses are highly flexible and so they are able to hide in the most interesting places, like the young octopus in the picture on the right hidden in a beer can. In contrary to most other cephalopods, octopuses mainly live in the benthic, on the ocean floor.

Like the Scylla from Homer's odyssey, octopuses like to hide in a cave and to reach into the surrounding water with their arms to catch crabs, snails and mussels, but also other octopuses. Octopuses, like other cephalopods, breathe with gills. That means they cannot survive on dry land for a long time. But they can stay there for a short period of time, which they use during low tide to hunt in tide pools. An octopus breathing, the pallial (mantle) cavity and siphon are well visible. Photo: Jim Cosgrove . Some octopus species also swim through open water, for example to get from one reef to the other. To do so, they move by pressing water from their pallial (mantle) cavity through the funnel, also called the siphon. Their eight arms are not used for swimming, which is why they are dragged behind. Swimming blue ringed octopus on flickr.com. Octopuses catch their prey in a similar way like other cephalopods, by help of their tentacles.

After they managed to do so, they prey is pulled towards the octopus' mouth opening, where the strong horn beak can bite a hole in the prey's armour ï¿½ most creatures octopuses prey on either have got a carapace (like crabs) or a shell (like snails, mussels and other molluscs). Then the octopus will liquefy its prey's interior organs and suck the resulting protein liquid. Giant octopus (Enteroctopus dolfleini) feeding on a crab. Picture: Sami Laine from kelpdiver.com . As a consequence, an octopus' hiding place will often be recognisable by the crab shells littering around it. When they have to defend themselves, some octopus species can deal painful bites: The blue ringed octopuses from the region of Australia are so poisonous, that each year there are accidents, because careless beach walkers get bitten, after they found such a small octopus in a tide pool and tried to pick it up. The remains of an octopus dinner. Octopuses also have got another, more defensive, weapon ï¿½ ink.

In a bladder-like organ branching off the intestine, they produce a black liquid, which is released in the surrounding water, forming a cloud. While the attacker deals with the fake octopus, the real thing gets time to escape after changing colour, camouflaging to fit the environment. Octopuses are very short-lived animals with a life-span of one or two years. Their life usually ends after mating and the hatching of the young. Whereas the male usually dies soon after mating, the female lives a bit longer to have time to watch over the eggs, until the young hatch. Sometimes the female octopuses live noticeably longer than the males. During copulation, the male transfers a spermatophore to the female, using one of its tentacles, specially formed to fit the task. Such a special tentacle is also called a hectocotylus. The female octopus will store the sperm in a special bladder organ, the Receptaculum seminis (sperm receptacle, see also: Genital apparatus of the Roman snail ). Later, usually separated from the process of mating by a space of time, the female will use those sperms to fertilise the egg cells, as soon as the environmental conditions are favourable.

Freshly hatched octopus larva. Photo: Jim Cosgrove . As long, as the young octopuses grow in their eggs, the mother will watch over the cave they are usually laid in, guarding them, cleaning them, supplying them with oxygen and occasionally defending them. In all this time, a female octopus will never leave its offspring, which is why she only eats very little. When the young octopuses have hatched, the mother often will die from weakness and exhaustion, as now she herself cannot defend anymore against her enemies. After hatching, the young octopuses thus are left to themselves, swimming in the open sea (the pelagic), in contrary to the adults living in the benthic. The losses to be expected are compensated by the high number of octopus offspring: Each batch of eggs may contain as many as 150,000 young octopuses. Picture: Robert Patzner , Salzburg University . Octopuses' nervous systems are very effective in different regards; their brain, octopuses being invertebrate molluscs, more than that of a fish, a vertebrate.

Especially highly developed centres are the optical lobes and the centres responsible for guiding the colour cells in the skin. Octopus eyes are the most advanced light sense organs among all invertebrates. An octopus has got lens eyes, generally equal to a vertebrate's eye, at its disposal. Mollusc eyes, however, evolved in another way than vertebrate eyes. The retina develops as a part of the eyeball and thus is innerved only later. So the light sense cells in the retina point into the inner space of the eyeball, towards the incident light. In that way a mollusc's everse eye is clearly different from a vertebrate's inverse eye, as in the latter the eye nerve grows into the eye only later, so the light sense cell point outwards, away from the light falling in. Also remarkable is the innervation of an octopus' tentacles. Male argonauts , for example, which also belong to the octopodids, are able to separate their hectocotylus, which then will find its way into the female's mantle cavity on its own (a fire-and-forget hectocotylus, so to speak). A giant octopus' tentacles.

Photo: Jim Cosgrove . Also tentacles involuntarily separated from the body (Argonauts are the only octopodids, which are able to voluntarily separate an arm) will continue to move on their selves. In general, octopuses do not have to guide all tentacle motions from the brain, but neural patterns stored in the tentacles allow at least for simple movements. A tentacle's suckers are also connected to nerves and they are provided with chemical sense cells, which give information on the matter touched. In the skin there are pigment cells (chromatophores) which can be guided separately. So apart from their highly flexible and changeable form, an octopus can also change its colour, an ability, in which octopuses have achieved mere mastership. The colour of their skin is not only used by octopuses as a means of camouflage, but also of communication with other of their kind. The blue ringed octopuses from Australia are called that way, because they display different kinds of blue ring patterns on their skin. But they only do so as a warning. Otherwise a blue ringed octopus' colour is a bleak yellowish brown.

It should be kept in mind, though, that octopuses, other than their squid relatives, are loners, which will defend their territory, eating also their smaller relatives, even their own kind. An octopus in a labyrinth. Source: Quarks & Co. (WDR). Apart from their effective nervous system, octopuses also are very good at learning things. They are able to remember colours and forms, as well as to find their way out of a labyrinth. It has been proven that octopuses can open closed boxes and uncork bottles to reach food. Octopuses also learn by watching a process without having tried it before. In an experiment on the learning abilities of octopuses it has been found that octopuses are able to connect colours with food given in the case of success, and that they also could remember simple forms. Octopuses kept in neighbouring tanks acquired that knowledge by observing their neighbours' progress in the experiment. Octopuses' learning abilities can be explained by their evolution in competition to other highly developed sea creatures. Octopuses also must be able to learn fast, as they have not ability to pass on their knowledge because of their low life span of maximally four years.

Also, because the mother dies after the young hatched, all abilities must be acquired freshly. A giant octopus (Enteroctopus dofleini). Picture: Sami Laine from kelpdiver.com . Octopuses are found in all seas on the Earth. Their size may reach from few centimetres to the Pacific giant octopus (Enteroctopus dofleini), which may measure four metres span width. Octopuses live in different habitats between the tidal zone and up to seven kilometres depth. In the Mediterranean there is for example the Common octopus (Octopus vulgaris) with a tentacle length of up to one metre and the little larger White Spotted octopus (Octopus macropus). Smaller species are the lesser octopus (Eledone cirrhosa) and the Musk octopus (Eledone moschata) with up to forty centimetres tentacle length. The largest known octopus is the Giant octopus (Enteroctopus dofleini) from the northern Pacific occurring on the American northwest coast. It may reach a tentacle length if more than two metres, there may even be specimens of more than three metres arm length, resulting in a seven metres span width.

In Australia and Southeast Asia there is the genus of blue ringed octopuses (Hapalochlaena). Those small octopuses (about ten centimetres tentacle length) are specially known for their characteristic warning colour, as well as for their highly poisonous venom. A blue ringed octopus' saliva contains tetrodoxin, a neural poison that will paralyse all conscious muscles killing the victim in less than a few hours. Most interestingly, it is produced not by the octopus, but by bacteria living in the salivary glands. In total, about 200 species of octopus are known to science, many of which, though, are not clearly specified. Difference Between Cuttlefish and Squid Home / Science & Nature / Nature / Animals / Difference Between Cuttlefish and Squid Difference Between Cuttlefish and Squid Posted on by Naveen Cuttlefish vs Squid When cuttlefish and squids are considered, the difference between them should be clearly understood, because someone would think that both these are the same. In fact, it has been a common mistake committed by many. Generally, cuttlefish are a group of marine animals and squids represent as a part of that group.

This article would be a great help for anyone with uncertainty about these two, as it clearly distinguishes the difference between them. Cuttlefish The term cuttlefish refers to many types of marine animals, including many taxonomic groups. However, as the name cuttlefish sounds like fish, someone would understand them as a fish variety, but they are not. In fact, cuttlefish is a group of marine molluscs belong to the Class: Cephalopoda. They mainly include squids, octopuses, and nautiluses. Usually, they have eight arms, two tentacles equipped with denticulate suckers, and large W-shaped pupils in eyes. In addition, they might have an internal bone (called pen) or an external shell depending on the subgroup characteristics. Since cuttlefish contains many taxonomic groups in the Class: Cephalapoda, they vary in a large range of sizes and bodyweights depending on the species. Usually, they feed on zooplankton including small molluscs, crabs, shrimp, fish, octopuses, worms, and other cuttlefish. They are remarkably intelligent among most of other invertebrates, as they have very large brain in relative to the body size.

Cuttlefish can camouflage well, and use it to prevent from the predators. Squid Squids are cephalopods belong to the Order: Teuthida. There are more than 300 species of them, and they are exclusively marine animals living in open seas. Squids have different sizes, and most of them are not more than 60 cm in body length, but the giant squids could be longer than 13 metres. Their exceptional swimming ability is noticeable, and on top of that, some species can even fly out of water for small distances. Squids have a distinct head, bilaterally symmetrical body, a mantle, and distinct arms projecting from one place (head). The structure of their body contains two long tentacles with eight arms arranged in pairs. The main body mass of the squids is enclosed inside their mantle except for the tentacles and arms. The underside of their body is lighter than the upper sides. Usually, squids can camouflage using their chromatophores on the skin; those enable to change the skin colour according to the environment. In addition, they have ink expulsion system, which helps to hide themselves from predators. What is the difference between Cuttlefish and Squid?

• Cuttlefish are a group of animals of the Class: Cephalapoda, while squids are a type of cuttlefish. • The biological diversity is higher among cuttlefish compared to squids, as it contains more taxonomic groups. • Some cuttlefish species have external shells, but squids have an internal bone-like structure called pen. Related posts: Cephalopods E-Fauna Funders and Sponsors MOLLUSCS OF BRITISH COLUMBIA Octopuses reach their largest size in the cool temperate waters of the north and south Pacific. Photo by James A. Cosgrove Introduction to the Cephalopoda James A. Cosgrove The Phylum Mollusca is one of the largest and most diverse of the animal groups. It contains more than 35,000 extinct and 130,000 living species in what are currently recognized as 7 unequal Classes. The name Mollusca comes from the Latin word mollis (meaning soft).

The word mollusc was first used by the French zoologist Cuvier in the late 1700’s to describe squids and cuttlefishes, members of the Class Cephalopoda. It was years later that the affinities between Cephalopods and the myriad of hard shelled animals such as clams and snails was recognized but by then the word mollusc was fixed and has remained to this day. The Class Cephalopoda is one of the most interesting groups as it possesses some of the most highly evolved non-vertebrates in the world. The word cephalopod comes from the Greek and means head/foot. When one looks at a squid or an octopus we see a ring of appendages surrounding a mouth and a head attached. Most of the squids and cuttlefishes are classified as decapods (10 appendages of which 8 are arms and 2 are tentacles) while most octopuses are octopods (8 arms only, no tentacles). Nautilus is the only modern cephalopod that has an external shell. It does not occur in BC. Photo courtesy of the Royal BC Museum.

Cephalopods are all marine and can be found in all oceans from the surface to as deep as 7 kilometers. Some cephalopods are pelagic and never touch land while others are benthic and live on the bottom all their lives. There are also intermediate forms that have pelagic larval forms and benthic adult forms. The cephalopods show a diversity of body forms. Some, such as nautilus and spirula, have external shells of calcium carbonate. The argonaut, however, produce a shell-like structure that is used to brood eggs in but the argonaut itself is a shell-less octopus. Cuttlefish have and internal skeleton called a “cuttlebone”. Squid also have a reduced internal skeleton of chitin called a “pen”. Octopuses have almost completely lost all skeletal elements and the only hard part in their body is the chitinous beak. Mating Opal Squid (Loligo opalescens). Photo by James A. Cosgrove Most cephalopods have a powerful saliva for digesting their meals and this may be injected into the food to partially digest the food before it is consumed.

Many cephalopods also have venom (cephalotoxin) that is used to incapacitate the food. This venom, in groups such as the Blue Ring Octopus of Australia and New Zealand, has been fatal to humans. Cephalopods have very short lives. Many of the smaller species will complete a full life cycle in less than 1 year. Even the largest of the pelagic squids have a life cycle of about 7 years. Many of the cephalopods are not well studied because they live at great depths and in the open ocean where research is very difficult and very expensive. For example, the first photos of a living Giant Squid (Architeuthis dux) in the wild were obtained in 2005 despite years of trying and millions of dollars being spent. One can understand how difficult it is for scientists to understand population dynamics or reproductive strategies in animals you only get to see when they wash up on shore or are caught by fishers. In most cases, cephalopods reproduce only once. When females reach sexual maturity they will mate and lay their eggs.

In some cases (nautilus, squids and cuttlefishes) the adults die right away and the eggs are left to the mercy of the ocean. In other cases (octopuses) the female will stay and brood the eggs until she dies. In most cases the octopus eggs will hatch before the female dies but it varies from individual to individual. One must recognize that cephalopod fisheries takes only pre-reproductive animals and those heavy effort fisheries have significantly impacted cephalopod populations in some parts of the world. Cuttlefish have an internal skeleton that is commonly used in bird cages. Cuttlefish are not found in B.C. Photo by James A. Cosgrove Cephalopods range in size from only a few grams to hundreds of kilograms. One of the most impressive features of the cephalopods is their skins. Most have the ability to rapidly change the colour and texture of their skin to serve a number of functions including camouflage, mimicry, alarm displays and various forms of communication. Living cephalopods are amazing to watch and that is one of the reasons why they are so popular in marine exhibits and home aquariums. Many species are, however, very difficult to keep in captivity.

Question: Squids, cuttlefish and octopus belong to which class of marine mollusc?
Answer: CEPHALOPOD